As microwave communications technologies continue their rapid progress, the demands for further miniaturization require continuing discovery and development of new materials. Dielectric materials useful for microwave resonators and filters must satisfy stringent physical property requirements. In the vicinity of ambient temperature, the materials should have a high dielectric constant (K), low dielectric loss (high Q), and low temperature coefficient of dielectric constant (TCK)--properties which are generally mutually exclusive. These requirements greatly restrict the availability of materials useful for actual devices. It is particularly important that the materials have low TCKs as devices used in microwave systems require high thermal stability.
There are currently several materials being developed for such use, e.g., based on barium titanates or tantalates and zirconium-tin titanate, with dielectric constants in the range of 20-90, Q values ranging from about 20,000 down to about 2,000 (materials having higher dielectric constants will have lower Q values), and TCKs of less than 10 ppm/.degree. C. See, e.g., P. K. Davies, "Materials and Processes for Wireless Communications," CERAMIC TRANSACTIONS Vol. 53 (American Ceramic Society, Ohio 1996), at p. 137, and T. Negas, G. Yeager, S. Bell, and R. Amren, "Chemistry of Electronic Ceramic Materials," NIST SPECIAL PUBLICATION, Vol.804 (1990), at p. 21. Bulk ceramics comprising Ba.sub.2 Ti.sub.9 O.sub.20, Ba.sub.6-3x Ln.sub.8+2x Ti.sub.18 O.sub.54, and Zr(Ti.sub.1-x Sn.sub.x)O.sub.4 are in use for macroscopic dielectric components employed in microwave communications devices, as disclosed in H. M. O'Bryan, J. Thomson, and J. K. Plourde, J. AM. CERAM. SOC. Vol. 57 (1974), at p. 450; T. Negas, G, Yeager, S. Bell and N. Coats, AM. CERAM. SOC. BULL. Vol. 72 (1993), at p. 80; and S. Nishigaki, H. Kato, S. Yano, and R. Kamimura, CERAMIC BULLETIN Vol. 66 (1987), at p. 1405. A dielectric material for use in a microwave resonator comprising barium oxide and titanium dioxide as the primary components is disclosed in U.S. Pat. No. 5,332,984 issued to Abe, et als., on Jul. 26, 1994, entitled "Dielectric Resonator or Filter for Microwave Application, and Method of Producing the Dielectric Resonator or Filter," which is incorporated by reference. Zirconium-tin titanate dielectrics having a TCK dependent on processing conditions are disclosed in R. Christoffersen, P. K. Davies, X. Wei, and T. Negas, J. Am. CERAM. Soc., Vol.77 (1994), at p. 1441.
As may be appreciated, those concerned with microwave communications systems and technologies continually search for new dielectric materials for use in such systems that have improved dielectric properties or offer the market a competitive choice among the materials available for use in these systems. The instant invention provides a dielectric material which has at least two embodiments comprising Ca.sub.5 Nb.sub.2 TiO.sub.12 or Ca.sub.5 Ta.sub.2 TiO.sub.12, wherein the titanium optionally may be partially substituted with zirconium; these materials have dielectric properties meeting the stringent requirements for microwave communications applications.